162 THE CARBOHYDRATES 



A substance known as artificial india-rubber* is produced 

 by kneading together a mixture of tri- and tetra-nitrocelluloses 

 partially dissolved in ether alcohol with castor oil. The 

 resulting substance may be made to have any degree of elas- 

 ticity, according to the materials which are mixed with it. 

 It forms a more or less satisfactory substitute for rubber and 

 possesses a high electric resistance. Though not explosive, it 

 is inflammable, but to do away with this inconvenience the 

 outer surface may be denitrated by treatment with alkali, 

 whereby it is rendered non-flammable. Artificial gutta-percha 

 is obtained by allowing an acetone solution of tetra-acetyl 

 cellulose to evaporate. 



Celluloid is produced by mixing the tri- and tetra-nitrates, 

 as employed for collodion, with camphor. 



Artificial Silks. These are produced in a variety of ways 

 by precipitating some form of cellulose from solution. The 

 first artificial silk was prepared by Chardonnet, who obtained 

 it by forcing collodion through fine nozzles ; the thin stream 

 of nitrocellulose solution on coming in contact with the air 

 solidifies to a thread by the rapid evaporation of the solvent. 

 To render it non-flammable the thread is denitrated by treat- 

 ment with ammonium sulphide. 



A second process for preparing artificial silk consists in 

 dissolving bleached mercerized cotton (see p. 151) in cupram- 

 monia solution. A fine stream of this solution is then run 

 into a dilute sulphuric acid, whereby a continuous thread of 

 cellulose is at once precipitated. 



A third process is that in which viscose solution is forced 

 through fine nozzles, the emerging streams being coagulated 

 either by hot air or by a bath of ammonium chloride. The 

 fine threads which result can be spun like silk. Cellulose 

 acetate also is used for this purpose. 



Viscose is obtained by acting on finely divided cellulose 

 with soda and treating the resulting substances with carbon 

 disulphide, whereby a cellulose thio-carbonate is produced; 

 this substance on exposure to air decomposes spontaneously 



*This substance must be carefully distinguished from so-called synthetic 

 rubber, which is an artificially polymerized hydrocarbon of the formula (C 5 H 8 )n ; 

 this substance, if not actually identical with natural rubber, is at any rate closely 

 related to it, whereas the artificial india-rubber mentioned above is a nitrated 

 cellulose, 





